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A class-5 telephone switch is a telephone switch or telephone exchange in the public switched telephone network located at the local telephone company's central office, directly serving subscribers. Class-5 switch services include basic dial-tone, calling features, and additional digital and data services to subscribers using the local loop. Class-5 switches were slower to convert from circuit switching technologies to time division multiplexing than the other switch classes. ==Telephone switch hierarchy== In order to organize direct distance dialing (DDD) American Telephone & Telegraph divided the various switches in the U.S. public switched telephone network (PSTN) into an "office classification" hierarchy containing five levels (classes). * ''Class-1'' exchanges were international gateways – handing off and receiving traffic from outside the USA and Canadian networks. * ''Class-2'' exchanges were tandem exchanges which interconnected whole regions of the AT&T network. * ''Class-3'' exchanges were tandem exchanges connecting major population centers within a particular region of the AT&T network. * ''Class-4'' exchanges were tandem exchanges connecting the various areas of a city or towns in a region. * ''Class-5'' exchanges were those to which subscribers and end-users telephone lines would connect. In modern times only the terms class-4 and class-5 are much used, as any tandem office is referred to as a class 4. This change was prompted by changes in the power of switches and the relative cost of transmission, both of which tended to flatten the switch hierarchy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Class-5 telephone switch」の詳細全文を読む スポンサード リンク
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